There is known a plasma processing apparatus using excitation of a processing gas by a microwave. For example, this plasma processing apparatus generates plasma by radiating the microwave generated by a microwave oscillator into a processing vessel and ionizing the processing gas within the processing vessel.
Further, as a technique for suppressing a deflection of an electric field which occurs within the processing vessel and is caused by a standing wave of the microwave, there is known a technique of generating a microwave having a preset frequency bandwidth by modulating a frequency of a carrier wave.
Patent Document 1: Japanese Patent Laid-open Publication No. 2012-109080